InGaAsP-InP Semiconductor Microcavity Geometries for Annular Bragg Reflection, Optical Switching, and Sensing

It was about 125 years ago that the light bulb was commercialized by Thomas Edison. No doubt a brilliant invention at the time, today its low power conversion efficiency is one of the reasons why lighting in the western world has such high energy consumption. Thus, the potential for saving energy is enormous in this area. The introduction of halogen, discharge and fluorescent lamps has lead to certain efficiency improvements, however more than half of the energy is still lost as heat. Light-emitting diodes (LEDs) are very promising candidates for high efficiency light sources, with modern devices showing internal quantum efficiencies of virtually 100 %. However, due to the high refractive index of the commonly used semiconductor materials it is very difficult to have a large extraction efficiency; in a standard cubic geometry most of the internally emitted light is trapped inside the device due to total internal reflection. Several methods have been developed in order to circumvent this problem, either by optimizing the device geometry in order to increase the escape cone or by incorporating a resonant structure in order to force the internal emission into the existing escape cone. The latter approach is called microcavity LED (MCLED) or resonant cavity LED (RCLED). In a MCLED the spontaneous internal emission is controlled by placing the emitter inside an optical cavity with a thickness of the order of its emitting wavelength. The resulting interference effects increase the part of the emission that can be extracted. Contrary to the other approaches this is possible without changing the device geometry and thus without additional costly back-end processing steps. The control of the farfield radiation pattern makes these devices particularly interesting for high brightness applications, which demand highly directional emitters, such as for printing, bar code reading, large area displays and optical communication. The extraction efficiency of a MCLED is inversely proportional to the effective cavity length. An ideal cavity, allowing an extraction efficiency close to unity, consists of a low refractive index material and has an optical length of λ/2. In contrast to this, to obtain high internal quantum efficiencies it is necessary to use high index cavities with an optical length of at least λ. It should be noted, that the large penetration depth of the optical field in the semiconductor-based distributed Bragg reflectors (DBRs) leads to a significant increase of the effective cavity length and thus further reduces the achievable extraction efficiencies. In this thesis novel concepts to reduce effective cavity lengths and therefore increase extraction efficiencies are implemented into standard MCLED structures. The phaseshift cavity principle whilst maintaining the electrical properties of a standard A cavity achieves optical properties approaching that of a λ/2 cavity. The use of AlOx instead of AlAs as the, low refractive index component in the DBRs leads to smaller penetration depths and a concomitant reduction of the effective cavity length. A similar effect can be obtained by combining a resonant cavity with a thin-film structure. Thanks to these design improvements, the external quantum efficiency of different types of MCLEDs was increased. Near infrared emitting InGaAs/GaAs MCLEDs including a phase-shift cavity were realized, as both bottom and top emitting structures. The external quantum efficiencies achieved for emission into air were 18 and 19 %, respectively. With the additional incorporation of an oxide based bottom DBR, the efficiency of top emitting near infrared MCLEDs was further increased to 28 %. Red emitting AlGaInP-based structures are not compatible with the phase-shift cavity principle. However the beneficial effect of the implementation of an oxide DBR is greater at their wavelength rather than in the near infrared. Thus with preliminary red emitting GaInP/AlGaInP MCLEDs containing a bottom oxide DBR external quantum efficiencies of 12% could be achieved. Unfortunately, the incorporation of an oxide DBR significantly complicates the device design and the device fabrication. These problems can be avoided by combining the resonant cavity with a thin-film structure instead. Initial non-optimized red emitting thin-film MCLEDs were realized by OSRAM Opto Semiconductors and characterized in this work. They show external quantum efficiencies of 23 % and 18 % with and without encapsulation, respectively. It is assumed that a significant fraction of the high external quantum efficiency is due to a strong photon recycling effect in these devices. Simulations presented in this thesis show that the theoretical limits for the MCLEDs discussed above are slightly higher than the values obtained, encouraging further device optimization. The thin-film MCLEDs seem to hold the biggest potential for high efficiency emission from MCLEDs, independent of the wavelength range of emission.

Advances in nanotechnology lead to the development of nano-electro-mechanical systems (NEMS) such as nanomechanical resonators with ultra-high resonant frequencies. The ultra-high-frequency resonators have recently received significant attention for wide-ranging applications such as molecular separation, molecular transportation, ultra-high sensitive sensing, high-frequency signal processing, and biological imaging. It is well known that for micrometer length scale, first-principles technique, the most accurate approach, poses serious limitations for comparisons with experimental studies. For such larger size, classical molecular dynamics (MD) simulations are desirable, which require interatomic potentials. Additionally, a mesoscale method such as the coarse-grained (CG) method is another useful method to support simulations for even larger system sizes. Furthermore, quasi-two-dimensional (Q2D) materials have attracted intensive research interest due to their many novel properties over the past decades. However, the energy dissipation mechanisms of nanomechanical resonators based on several Q2D materials are still unknown. In this work, the addressed main issues include the development of the CG models for molybdenum disulphide (MoS2), investigation of the mechanism effects on black phosphorus (BP) nanoresonators and the application of graphene nanoresonators. The primary coverage and results of the dissertation are as follows: Method development. Firstly, a two-dimensional (2D) CG model for single layer MoS2 (SLMoS2) is analytically developed. The Stillinger-Weber (SW) potential for this 2D CG model is further parametrized, in which all SW geometrical parameters are determined analytically according to the equilibrium condition for each individual potential term, while the SW energy parameters are derived analytically based on the valence force field model. Next, the 2D CG model is further simplified to one-dimensional (1D) CG model, which describes the 2D SLMoS2 structure using a 1D chain model. This 1D CG model is applied to investigate the relaxed configuration and the resonant oscillation of the folded SLMoS2. Owning to the simplicity nature of the 1D CG model, the relaxed configuration of the folded SLMoS2 is determined analytically, and the resonant oscillation frequency is derived analytically. Considering the increasing interest in studying the properties of other 2D layered materials, and in particular those in the semiconducting transition metal dichalcogenide class like MoS2, the CG models proposed in current work provide valuable simulation approaches. Mechanism understanding. Two energy dissipation mechanisms of BP nanoresonators are focused exclusively, i.e. mechanical strain effects and defect effects (including vacancy and oxidation). Vacancy defect is intrinsic damping factor for the quality (Q)-factor, while mechanical strain and oxidation are extrinsic damping factors. Intrinsic dissipation (induced by thermal vibrations) in BP resonators (BPRs) is firstly investigated. Specifically, classical MD simulations are performed to examine the temperature dependence for the Q-factor of the single layer BPR (SLBPR) along the armchair and zigzag directions, where two-step fitting procedure is used to extract the frequency and Q-factor from the kinetic energy time history. The Q-factors of BPRs are evaluated through comparison with those of graphene and MoS2 nanoresonators. Next, effects of mechanical strain, vacancy and oxidation on BP nanoresonators are investigated in turn. Considering the increasing interest in studying the properties of BP, and in particular the lack of theoretical study for the BPRs, the results in current work provide a useful reference. Application. A novel application for graphene nanoresonators, using them to self-assemble small nanostructures such as water chains, is proposed. All of the underlying physics enabling this phenomenon is elucidated. In particular, by drawing inspiration from macroscale self-assembly using the higher order resonant modes of Chladni plates, classical MD simulations are used to investigate the self-assembly of water molecules using graphene nanoresonators. An analytic formula for the critical resonant frequency based on the interaction between water molecules and graphene is provided. Furthermore, the properties of the water chains assembled by the graphene nanoresonators are studied.

Balanced radiation and absorption rates of an optical resonator are necessary for coherent perfect light absorption in many active device applications. This balance is referred to as critical coupling condition. We propose a gain-assisted method for exact access to critical coupling conditions without altering any structure parameters. In a coherent absorber with additional internal gain media, critical coupling with arbitrarily high coherent signal extinction can be obtained by continuously tuning optical pumping density. Assuming a surface-plasmon resonance grating covered by a gain layer as a promising architecture, we numerically demonstrate gain-assisted continuous access to its critical coupling point with experimentally probable settings. In addition, the gain tuning further introduces switching of the coherent-absorber's functionality to a conventional lossless beam splitter.

The superfluid state, often obtained in the laboratory using liquid helium at very low temperatures, provides the basis for a wide range of interesting experiments. One large field of research relates to the study of turbulence in a superfluid, referred to as quantum turbulence due to the importance of quantum mechanical behaviour in the description of this phenomenon. An important experimental tool in the study of quantum turbulence is the mechanical resonator, with many different types of oscillator seeing use. Variations in the resonance can be related to the properties of the fluid through an understanding of the drag applied to the object. The many seemingly disparate measurements reported here were performed in the hope of providing background for future development of improved experimental techniques. In an effort to develop an improved method for determining oscillator properties, measurements have been made using a multifrequency lock-in amplifier in superfluid 4He. The results obtained show that the multifrequency lock-in can be used to obtain results equivalent to the traditional method while reducing the time required. Due to the possibility of vastly increased sensitivity to changes in effective mass, tests were performed in 4He using a new form of oscillator with a 100 nm by 100 nm square cross-section, significantly smaller than other available devices. The resonant frequency of these resonators, referred to as nanobeams, was varied from 0.6 MHz to 8.5 MHz by using beams of different length. Measurements of the resonator response as a function of temperature show that the beams can successfully probe the fluid, though the current theory is found to be insufficient to exactly quantify the dependence seen. A possible observation of turbulence generated by a nanobeam is also reported. Despite an observed critical velocity significantly different to theoretical predictions, all other measurements are consistent with a turbulent transition. As the eventual goal is to use nanobeams for measurements in 3He-B, the drag on high frequency oscillators in 3He-B was also studied. Measurements on 4 devices of different frequencies found that the current model of damping remains adequate beyond the expected frequency limit for this model. Observations of anomalous increases in the damping for a single resonator in 3He-B are also discussed. As this unexpected damping is only seen for small, sensitive resonators there is concern that similar effects could hinder interpretation of future nanobeam measurements in 3He-B. Efforts were made to understand the source of this damping, and hence explain why it is seen for only one of three nominally identical oscillators, though no conclusive explanation could be found.

Mechanical resonators are used in a wide variety of technical applications, from precision time keeping and sensing, to the delay and filtering of microwave signals in mobile communication systems. Critical to many of these applications is the ability of a mechanical object to store vibrational energy at a well defined frequency of oscillation and with minimal damping. Energy damping can occur through acoustic radiation into the resonator support structure, or through impurities and defects in the resonator material, and is highly dependent on the temperature of operation due to the inherent anharmonic motion of atoms within solid-state materials. Here, we present optical measurements down to milliKelvin temperatures of the acoustic mode properties of a crystalline silicon nanobeam cavity incorporating a three-dimensional phononic bandgap support structure for acoustic confinement. Utilizing pulsed laser light to excite a co-localized optical mode of the optomechanical crystal (OMC) device, we are able to measure the dynamics of the internal cavity acoustic modes which are coupled to the light field via radiation pressure. These measurements represent an almost ideal scenario in which the ringdown occurs free of any additional mechanical or probe field contact, and where elastic scattering or radiation of the acoustic field does not lead to energy damping due to the full bandgap shield. The resulting ringdown measurements for the fundamental 5 GHz acoustic mode of the cavity show an exponential increase in phonon lifetime versus phononic shield period number, which at a bath temperature of 35 milliKelvin saturates above six periods to a value as long as 1.5 seconds. This ultra-long lifetime, corresponding to an effective phonon propagation length of several kilometers, is found at the lowest temperatures to be consistent with damping from non-resonant tunneling states whose energy lies below the acoustic shield phononic bandgap, and which are most likely present in the amorphous etch-damaged region of the silicon surface. Other, more rapid forms of damping such as resonant tunneling state damping or three-phonon scattering are suppressed due to the phononic bandgap shield and the reduced density of phonon states in the effectively one-dimensional nanobeam geometry. Prospects for newapplications of ultra-coherent nanoscale mechanical resonators include tests of various collapse models of quantum mechanics, or, if appropriately integrated with microwave superconducting quantum circuits, as miniature quantum memory or processing units with potentially many-orders of magnitude longer coherence time than their electromagnetic counterparts.

Based on the linear property of silicon microring resonators, we experimentally observed that such resonator can transform square-wave signal into pulse-wave signal, and the output waveform is strongly dependent on the input wavelength. We then proposed a mathematical model, which utilized linear coupling mode theory, Fourier transform and electro-optical Mach-Zehnder (MZ) intensity modulation functions. The numerical simulation results fit well with the experimental results. Besides, we gave a detailed explanation based on the transfer function of microrings. Furthermore, we have studied the case when the ring resonator is deviated from the critical coupling condition, and found that the coupling state, over coupling or under coupling, can be easily judged through the output waveform.

Many applications require the presence of a dielectric inside a microwave resonator. The paper presents an analysis based on the mode-matching technique of a dielectric-loaded cavity that has a configuration which is more generalised than that first proposed by Amman and Morris. The cavity consists of a wave guide of rectangular cross-section filled with dielectric for part of its length and also for part of its transverse dimension, with movable shorting plungers in the guide beyond both ends of the dielectric. Such a structure supports resonances at frequencies where a particular waveguide mode is above cutoff inside the dielectric, but is below cutoff outside. Frequency tuning is possible via the tunable plungers. Computed results for the resonant frequencies and unloaded Q-factors are presented for anumber of cavity configurations. Close corroboration of the predicted resonance frequency by experiment has been obtained. Furthermore, the performance of a Gunn-effect diode oscillator employing such a dielectric-loaded cutoff waveguide cavity as the frequency stabilising agent is investigated experimentally.

In this study, a low-power and low-voltage 5.5-GHz receiver front-end circuit is designed using a resonator coupling technique. An on-chip transformer combined with the parasitic capacitances from a low-noise amplifier (LNA), a mixer, and the transformer itself comprises two coupled resonators of the resonator coupling network (RCN). The RCN functions as a balun, and couples energy from the LNA to the mixer. Under the critical coupling condition, the RCN gives a maximal current gain at resonance frequencies, equivalent to the same level by an ideal transformer. The analysis shows that the current gain is quite tolerable to the coupling coefficient variation, an advantageous feature for on-chip transformer design. The technique is verified by the receiver front-end in 0.18-μm CMOS technology. The RCN possess a current gain as high as 12 dB at 5.5 GHz. The measured input return loss, conversion gain, and third-order intermodulation intercept point of the entire circuit are 16 dB, 17.4 dB, and -1.5 dBm, respectively. The noise figure is 7.8 dB at the IF frequency of 1 MHz. The power consumption is only 0.33 mW from a 0.6-V supply. The required local oscillator power is only -9.5 dBm. This receiver front-end successfully demonstrates the resonator coupling technique.

A new class of planar optical components and devices has emerged using subwavelength metastructures with a strong contrast in refractive indices. High-contrast metastructures have shown promises to manipulate optical fields in an extraordinary way and to replace conventional bulky optical elements by their low-profile analogs, typically with subwavelength-scale features. We elucidate the underlying principle, how these seemingly low-profile geometries render unique optical responses, using the coupled-mode analysis in a multimode waveguide. Moreover, strong field localization in high-index structures allows us to interpret each single element in the metastructures as a low-quality-factor resonator (or a localized scatterer), permitting us to realize designer surface that shapes phase, amplitude, and polarization of light in free space, also known as an optical metasurface. The remainder of the thesis is devoted to explore novel applications in optics using high-contrast metastructures. One of the particularly interesting applications is to use them in an optical resonator. Specifically, we demonstrate to incorporate high-contrast subwavelength grating reflectors and dielectric metasufaces in a vertical Fabry–Perot cavity, and show that we can flexibly tune the resonance frequency by the subwavelength patterning. With this technique, we envision the realization of compact, on-chip spectrometers when integrating them on a photodetector array. Secondly, we investigate the use of high-contrast subwavelength gratings in visible wavelengths. We perform the optimization of their geometries and demonstrate a set of RGB color filters, down to near a micrometer in the pixel size. This platform exhibits unique performances such as high efficiency, angular insensitivity, and color tunability by the design. A novel device concept is also explored, where a high-contrast subwavelength grating reflector is integrated on a silicon platform to constitute an active resonant antenna, enabling high-speed, phase-dominant modulation by means of thermo-optic effect of silicon. We demonstrate an array of such active antennas, yielding a beam deflection capability. This justifies the robustness of our device design, enabling a large-scale integration of high-speed, phase-dominant spatial light modulators. Finally, we introduce a disorder-engineered metasurface in the context of wavefront shaping. Recently, wavefront shaping with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics, but translating this class of technology into a practical use has remained challenging due to enormous amounts of information needed to be characterized as the input-output responses. As a paradigm shift, we propose the use of disorder-engineered metasurface in wavefront shaping, where the disorder is programmatically designed and makes the system characterization-free prior to use. With this approach, we demonstrate high numerical aperture focusing in an extended volume as well as wide-field fluorescence imaging with unprecedented performances.

An acoustic metamaterial consisting of a homogeneous damped plate with parallel attached resonators is presented. Theoretical analysis shows that the metamaterial plate can generate multiple resonant-type band gaps and the lower-bound frequency of each band gap coincides with the resonance frequencies of the resonators. The parallel arrangement of resonators, compared with the metamaterial plate with resonators attached in series reported by Peng et al. (2015), results in a wider second band gap with a lower edge, while the first band gap is almost the same, creating therefore an easier combination of the multiple band gaps into a wider one. It is noted that damping has a significant influence on the band gaps and the effective mass density (especially for the damping of resonators). Specifically, it can be concluded that damping cannot be neglected in practical engineering applications, damping in the material of the host plate can smooth and lower the responses in the whole frequency range, especially in the higher frequency range, and a high level of damping of resonators deactivates the effect of band gaps. Such weak/damped resonators actualise the metamaterial damping poorly, and rather tend only to contribute to the overall damping such as the damping of the host plate.

A general strategy for the fabrication of nanoscopic light sources is presented. In these high-index-contrast materials, light is confined and its intensity is enhanced on the nanometer scale because of the large discontinuity of the electric field at high-index-contrast interfaces. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

One of the major concerns in the operability of power generation systems is their susceptibility to combustion instabilities. In this work, we aim to examine the effective use of heat exchangers, an integral component in any power generation system, to passively control combustion instability. The combustor is modelled as a quarter-wave resonator (1-D, open at one end, closed at the other) with a compact heat source within, which follows time lag law for heat release. The heat exchanger (hex) is modelled as an array of tubes with bias flow and is placed near the closed end of the resonator, causing it to behave like a cavity-backed slit plate: an effective acoustic absorber. For simplicity and ease of analysis, we treat the physical processes of heat transfer and acoustic scattering occurring at the hex as two individual processes separated by an infinitesimal distance. The aeroacoustic response of the tube array is modelled using a quasi-steady approach and the heat transfer across the hex is modelled by assuming it to be a heat sink. Unsteady numerical simulations were carried out to obtain the heat exchanger transfer function (HTF), which is the response of the heat transfer at hex to upstream velocity perturbations. Combining the aeroacoustic response and the HTF, in the limit of the infinitesimal distance between these processes tending to zero, gives the net influence of the hex. Other parameters of interest are the heat source location and the cavity length (the distance between the tube array and the closed end). We then construct stability maps for the first resonant mode of the aforementioned combustor configuration, for various parameter combinations. Preliminary observations show that stability can be achieved for a wide range of parameters.

Harmonic oscillators might be one of the most fundamental entities described by physics. Yet they stay relevant in recent research. The topological properties associated with exceptional points that can occur when two modes interact have generated much interest in recent years. Harmonic oscillators are also at the heart of new quantum technological applications: the long lifetime of high-Q resonators make them advantageous as quantum memories, and they are employed for narrowband processing of quantum signals, as in Josephson parametric amplifiers. The goal of this thesis is to explore different fundamental regimes of two coupled harmonic oscillators using cavity optomechanics as the experimen- tal platform. With consistent progress in attaining ever increasing Q factors, mechanical and electromagnetic resonators realize near-ideal harmonic oscillators. By parametrically modulating the nonlinear optomechanical interaction between them, an effective linear coupling is achieved, which is tunable in strength and in the relative frequencies of the two modes. Thus cavity optomechanics provides a framework with excellent control over system parameters for the study of two coupled harmonic modes. The specific optomechanical implementation employed are superconducting circuits with the vibrating top plate of a capacitor as the mechanical element. Multimode optomechanical circuits are realized, with two microwave modes interacting with one or two mechanical oscillators. The supplementary modes serve either as intermediaries in the relation of the two modes of interest, or as auxiliaries used to control a parameter of the system. Three main experimental results are achieved. First, an auxiliary microwave mode allows the engineering of the effective dissipation rate of a mechanical oscillator. The latter then acts as a reservoir for the main microwave mode with which it interacts. The microwave mode susceptibility can be tuned, resulting in an instability akin to that of a maser and in resonant amplification of incoming microwave signals with an added noise close to the quantum minimum. Second, we study the conditions for a nonreciprocal interaction between two microwave modes, when the information flows in one direction but not in the other. The two modes interact through two mechanical oscillators, leading to frequency conversion between the two cavities. Dissipation in the mechanical modes is essential to the scheme in two ways: it provides a reciprocal phase necessary for the interference and eliminates the unwanted signals. Third, level attraction between a microwave and a mechanical mode is demonstrated, where the eigenfrequencies of the system are drawn closer as the result of interaction, rather distancing themselves as in the more usual case of level repulsion. The phenomenon is theoretically connected to exceptional points, and a general classification of the possible regimes of interaction between two harmonic modes is exposed, including level repulsion and attraction as special cases.

In this article, we investigate the tuning and miniaturization performance induced by a volume perturbation inserted in a cavity resonator. The volume perturbation is either a rectangular perturbation centrally located, called central postperturbation (CPP) or dually, a hole shaped in an annular extruded volume, called side annular perturbation (SAP). The tuning and miniaturization mechanism is fully described using the small perturbation theory. This serves the analytical evaluation of the frequency shift resulting from the insertion of the perturbation volume in the cavity resonator. The impact of these perturbations is assessed also by HFSS simulations and measurements of 72 different cavity resonators. An idle cavity resonator characterized by a resonance frequency of 4 GHz is tuned from 1 to 6 GHz. A maximal frequency shift of 3 GHz and 2 GHz is measured for respectively the resonator with CPP and SAP, resulting in a total tuning range of 125%. Additionally, the CPP serves miniaturization purposes, as cavity resonators with a resonance frequency as low as 1 GHz were measured, derived from an idle cavity resonator at 4 GHz. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:491–496, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26578

Provide a proof of concept for the potential of using a novel RF resonant cavity device for accurately and repeatedly measuring fat and fat-free masses in phantom infants. Design, construct, and characterize an RF resonant cavity with dimensions compatible to holding an infant. The cavity was characterized using spherical phantoms of 0%fat, 50% fat, and 100% fat to empirically calibrate shifts in resonant frequency. The phantoms were constructed using emulsions of bovine lard, water, and dish soap inside spherical containers which do not interact with the electric field. The calibration phantoms were compared with a phantom of a test sample to assess the ability of the resonant cavity perturbation technique for measuring body composition. Phantoms of distinct %fat (0%, 50%, and 100%) were used to calibrate the resonant cavity for measuring body composition. The calibration phantoms were used to create calibration lines of unique %fat and were compared to a 475-mL sample of unknown %fat as a measure of how accurate the resonant cavity technique is for measuring body composition. A 475mL test sample was used to examine the robustness of the RCP technique. The sample was 25% fat and had a fat mass of ( )g. The measured fat mass from the RCP technique was g, or a 2% difference. The resonant cavity perturbation technique provides an accurate and repeatable measurement of fat mass in spherical phantoms and suggests the technology might be an effective obesity research tool for infants. Future studies will focus on extending the work to more complex anthropomorphic shapes.